Rotary compressor control system

ABSTRACT

New and improved rotary compressor control means are provided and include means to prevent restarting of the compressor motor against a high-pressure load in the compressor discharge system, and means to maintain a flow of air through the compressor during unloaded operation of the latter. In addition, means are provided to substantially attenuate the operational noise level of the compressor, and the discomforting effects thereof upon operating personnel.

I United States Patent l 13,ss2,233

[72] Inventor Carl Bloom 2,345,797 3/1943 Corson 230/6 Springfield, Mass. 3,072,320 1/1963 Cox et al 230/210 [2!] Appl. No. 819,011 3,186,631 1/1965 Lamberton et al. 230/207 [22] Filed Apr, 24, I969 3,260,444 7/1966 Williams et a1. 230/207 [4ft] faueqlgd June I, I071 3,349,994 l0/l967 Bloom 230/24 [73] Assignee Woflhlngum Corporllkm 3,448,916 6/1969 Fraser 230/24 Harrison Primary ExaminerWilliam L. Freeh Attorney-Daniel H. Bobis [54] ROTARY COMPRESSOR CONTROL SYSTEM 22 Claims, 7 Drawing Figs.

[52] US. Cl 417/12,

417/174l7/26418/l004l7/279 ABSTRACT: New and improved rotary compressor control [51] Int. Cl F04b 49/00 means are provided and include means to prevent restarting of [50] Fleld of Search 230/6, 17, the compressor motor against a high pressure load in the 207, 208; 417/17, 27, 2 418/100 pressor discharge system, and means to maintain a flow of air through the compressor during unloaded operation of the [56] References cued latter. In addition, means are provided to substantially attenu- UNITED STATES PATENTS ate the operational noise level of the compressor, and the 2, 941 l2 i lg V 230/25 discomforting effects thereof upon operating personnel.

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CARL BLOOM 1 ROTARY COMPRESSOR CONTROL SYSTEM BACKGROUND OF THE INVENTION This invention relates to a new and improved control system for rotary compressors and, more particularly, to a rotary compressor control system for controlling, in interrelated manner, the loading and unloading thereof and the starting and stopping of the compressor.

Although a wide variety of rotary compressor control systems are known for controlling the loading and unloading of the compressor, and the starting and stopping thereof, it may be understood that, in general, there are certain not insignificant disadvantages inherent in the design and/or manner of operation thereof. More specifically, in many of the prior art rotary compressor control systems, it may be understood that the compressor is subjected to excessively frequent compressor motor starts with resultant damage to the latter and/or decrease in the operational life thereof.

Too, in many instances, the compressor is required to frequently restart against a high-pressure load in the compressor discharge system with resultant possibility of damage to the blades of the rotary compressor, and undesirable high initial torque demand and attendant and similarly undesirable high initial electrical power demand on the electrical system which powers the compressor. In addition, many of the prior art rotary compressor control systems substantially discontinue the flow of air through the compressor during unloaded operation thereof with resultant undesirable effect upon the compressor lubrication system and the operation of compressor safety devices in the nature, for example, of discharge air temperature sensing means.

Another problem which arises in part from this substantial discontinuance of airflow during unloaded operation, and in part from the direct bleeddown of high-pressure compressor system components to atmosphere, is the very significant problem of high operational noise level and the aggravation and general discomfort caused thereby on operating personnel.

Further, although a variety of solutions in the nature, for example of electrical timer means have been proposed in the prior art for solving the problem of excessive compressor motor starts and/or the problem of requiring compressor restarting against a high-pressure load, it may be understood that, in general, such solutions have proven inordinately expensive and/or insufficiently reliable for long term operation under demanding operational conditions.

OBJECTS OF THE INVENTION It is, accordingly, an object of this invention to provide a new and improved rotary compressor control system which prevents excessive compressor motor starts.

Another object of this invention is the provision of a rotary compressor control system as above which prevent compressor restarts against high-pressure loads in the compressor discharge system.

Another object of this invention is the provision of a rotary compressorcontrol system as above which functions to provide for some flow of air through the compressorduring unloaded operation to insure adequate compressor lubrication and effective operation of compressor safety devices.

Another object of this invention is the provision of a rotary compressor control system as above which substantially reduces the operational noise level of the compressor and the aggravating effects thereof upon operating personnel.

A further object of this invention is the provision of a rotary compressor control system as above which requires the use of only readily available components of proven dependability in the fabrication thereof to thus provide for long periods of satisfactory, maintenance-free control system operation under demanding operational conditions.

A still further object of this invention is the provision of a rotary compressor control system which provides all of the sig nificant advantages stipulated above at relatively low cost.

SUMMARY OF THE INVENTION As currently preferred the new and improved rotary compressor control system of the invention is for application to a rotary compressor having a compressor suction control for loading and unloading the compressor, an oil air tank connected to the compressor discharge for compressor lubrication purposes, an air storage tank connected to the discharge of the oil air tank, and pressure responsive control means operatively associated with the air storage tank and the ener' gization circuit for the compressor motor and effective to respectively operate the compressor suction control to load and unload said compressor, and to start and stop said com- I pressor motor, in response to the pressure in the air storage tank. For such use, the control system of the invention comprises a restricted conduit which is effective, upon compressor-unloading operation of the pressure responsive control means, to bleeddown the oil air tank through the compressor suction control at a predetermined rate, and an air injection conduit which is concomitantly operable to inject air into the compressor inlet to maintain a flow of air through the compressor during unloaded operation thereof. Further included in the system of the invention are pressure responsive means which are operatively associated with the oil air tank and are operable to prevent stopping of the compressor by the pressure responsive control means until the pressure in the oil air tank has been bled down to a predetermined level. In an alternate form, the system of the invention comprises a variable restriction in the oil'air tank bleeddown conduit, and said variable restriction is effective to bleeddown the oil air tank at a variable rate in accordance with the pressure in the latter.

DESCRIPTION OF THE DRAWINGS The above and other objects and advantages of this invention are believed made clear by the following detailed description thereof taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic flow diagram of a representative, ro-

tary compressor control system constructed and operative in accordance with the teachings of the prior art;

FIG. 2 is a circuit diagram of the control circuit for use with the control system of FIG. 1;

FIG. 3 is a schematic flow diagram of a first form of a rotary compressor control system constructed and operative in accordance with the teachings of this invention;

FIG. 4 is a circuit diagram of the control circuit for use with the control system of FIG. 3;

FIG. 5 is a schematic flow diagram of a second form of a rotary compressor control system constructed and operative in accordance with the teachings of this invention;

FIG. 6 is a longitudinal cross-sectional view taken through the controlled restriction bleeddown valve of the system of FIG. 5 in a first position thereof; and

FIG. 7 is a longitudinal cross-sectional view taken through the controlled restriction bleeddown valve of FIG. 5 in a second position thereof.

DESCRIPTION OF THE PRIOR ART Referring initially to the representative, prior art rotary compressor control system of FIG. 1, the same may be seen to include a rotary compressor 10 comprising conventional compressor suction control means 12 which are, of course, effective to load and unload the former. The suction control means 12 include a compressor air inlet conduit 13 connected thereto, and suitable air filter means 14 are connected as shown in the said air inlet conduit for obvious purpose.

A discharge conduit 15 connects the discharge of the rotary compressor 10 to an oil air tank 16, and demister means 18 are operatively associated with the latter in conventional manner.

An air storage tank is indicated at 20, and a conduit 22, including a check valve 24 connected therein as shown, connects the demister 18 to the said air storage tank.

A double contact, normally closed pressure switch is indicated at PS-A and may be seen to be operatively connected to the air storage tank 20 by conduit 26 so as to be responsive to the pressure in the former. A three-way solenoid valve is indicated at 28 and is connected as shown, by conduits 30 and 32, respectively, to the air storage tank 20 and the compressor suction control means 12. The three-way solenoid valve 28 includes a vent port as indicated at 33 which is effective to vent the same to atmosphere.

An oil air tank bleeddown valve is indicated at 34 and is connected as shown to the demister 18 by a conduit 36, and to the conduit 32 by a conduit 38. The said bleeddown valve includes a bleed port 40 which is effective to bleed the valve to atmosphere.

Temperature responsive electrical switch means are indicated at 41 and may be understood to be operatively connected in the compressor discharge, just downstream of the compressor discharge ports, to sense air discharge pressure.

The control circuit for the prior art, rotary compressor control system of FIG. I is depicted in FIG. 2 and may be seen to include normally closed contacts 42 of the pressure switch PS-A, the operating solenoid 44 of the three-way solenoid valve 28, and suitable motor starter interlock means 46, to break current to the solenoid on shutdown to bleed the unit which are respectively connected as shown in series across the line sources 52 and 54 by leads 48 and 50.

Further included in this control circuit are the normally closed contacts 58 and 60 of suitable, motor overload responsive safety devices, the normally closed contacts 62 of the temperature responsive switch means 41, the compressor motor starter means 64, and the pole 68 and constant speed contact 70 of a two-position selector switch 72, respectively all of which are connectable in series across the line sources 52 and 54 by leads 74 and 76 and the switch pole 68 when the selector switch 72 is in the constant speed position thereof. The start-stop contact 78 of the two-position selector switch 72, and the remaining normally close contacts 80 of the pressure switch PS-A are connected as shown in series by lead 82 which is in turn connectable in series with leads 48 and 74 across the said line sources through the switch pole 68 when the selector switch 72 is in the start-stop position thereof.

The three-way solenoid valve 28 is arranged in the flow diagram of FIG. 1 to connect conduits 30 and 32 when the valveoperatingsolenoid 44 is deenergized and it may be understood that this will be effective to supply a pressure signal from the air storage tank 20 to the suction control means 12 to close the latter and unload the rotary compressor 10, and to concomitantly supply a pressure signal therefrom to the oil air tank bleeddown valve 34 to connect conduit 36 with the bleeddown valve port 40 to bleeddown the oil air tank 16.

With the valve-operating solenoid 44 of valve 28 energized, it may be understood that the three-way solenoid valve 28 will be elTective to vent conduit 32, and accordingly conduit 38, to atmosphere through vent port 33 with the results that the compressor suction control will reopen to reload the compressor, while the oil air tank bleeddown valve 34 terminates the bleeddown of the oil air tank 16 through conduit 36.

In the operation of the prior art compressor control system of FIGS. 1 and 2 with the selector switch 72 in the start-stop position thereof, pressure switch PS-A will be set to open switch contacts 42 and 80 in response to a predetermined pressure in air storage tank 20. As this occurs, the motor starter 64 will be deenergized through the opening of switch contacts 80 in lead 82 to stop the compressor 10. Concomitantly, the opening of switch contacts 42 in lead 50 will effect the deenergization of the valve-operating solenoid 44 whereby the solenoid valve 28 will operate the suction control 12 to unload the compressor while commencing the bleeddown of the oil air tank 16 to atmosphere through bleeddown valve port 40.

If, on the one hand, the pressure in the air storage tank is suddenly and markedly reduced, as by a sudden large scale demand for compressed air well before oil air tank bleeddown has been completed, it may be understood that the resultant reclosing the contacts and 42 of PS-A will force the compressor 10 to restart against a large pressure load in the said oil air tank to require a very high starting torque with resultant possibility of damage to the compressor motor and/or to the plant electrical system as a result of this sudden high power demand on the latter. In addition, it is believed clear that such restarting of the rotary compressor 10 against a high-pressure load in the compressor discharge system may, of course, result in damage to one or more of the compressor blades. Too, it may readily be understood that with the control system being effective to immediately restart the compressor 10 every time the pressure in air storage tank 20 falls below a predetermined minimum pressure, excessive restarting of the compressor motor with attendant damage thereto and/or decrease in the operational life thereof, will most probably result.

If, on the other hand, the oil air tank 16 is enabled to bleeddown to atmosphere, there being substantially no flow of air through the compressor 10 when the latter operates unloaded, it may be understood that the pressure therein will become insufficient to immediately supply adequate lubrication to the compressor 10 upon subsequent restarting of the latter, thus giving rise to the possibility of damage to the compressor, from inadequate lubrication resulting from repeated restarting under such conditions.

In addition, and under either of the above circumstances, it may be understood that the operational noise level of the compressor 10 is markedly increased, and/or the effect thereof upon operating personnel markedly aggravated, by the bleed of the oil air tank directly to atmosphere through bleeddown valve port 40, and by the change in pitch of the operational noise of the compressor 10 as the latter cycles between loaded and unloaded operation. Too, the substantial lack of airflow through the compressor 10 during unloaded operation thereof will materially decrease the effectiveness of the temperature sensing switch means 41 under such conditions, as should be obvious.

Further, although the setting of the selector switch 72 to the constant speed position thereof will prevent excessive compressor motor restarting against high compressor discharge system pressure loads, it will not compensate for the other significant disadvantages enumerated above, and further, will require increased electrical power since the compressor motor will be operating constantly.

One solution which has been proposed for solving the problems encountered during start-stop operation of a prior art compressor control system asdescribed above is the incorporation therein of electrical timer means to provide for a predetermined time delay between the opening of contacts 80 of PS-A and the stopping of the compressor motor. The use of such timer although generally satisfactory may, however, be readily understood to give rise to other significant disadvantages in the nature of excessive timer costs and the lack of absolute reliability thereof for long periods of operation under demanding operational conditions.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the new and improved rotary compressor control system constructed and operative in accordance with the teachings of this invention as depicted in FIG. 3, the same may be seen to be applied to the control of a rotary compressor which may, for example, take the form of that manufactured and marketed under the model designation RS Mono Rotor Air Compressor" by applicants assignee, The Worthington Corporation of Harrison, New Jersey. The rotary compressor 90 comprises compressor suction control means 92, including a closure disc 94, which is actuable in conventional manner by a plunger rod 96 to load and unload the said compressor. The suction control means 92 comprise a compressor air inlet conduit 98 connected thereto, and suitable air filter means 100 are connected therein as shown for obvious purpose.

A discharge conduit 102 connects the discharge of the rotary compressor 90 to operatively associated oil air tank and demister means104 and 106, respectively, and a temperature sensitive switch as indicated at 108 is disposed as shown at the compressor discharge just downstream of the compressor discharge ports to sense the temperature of the compressed air discharged therefrom.

An air storage tank is indicated at 110, and a conduit 112, including a check valve 114 connected therein as indicated, connects the demister 106 to the said air storage tank.

A double contact, normally closed pressure switch is indicated as PS-B and is connected as shown by conduit 116 to the air storage tank 110 so as to be responsive to the pressure in the latter.

A three-way solenoid valve is indicated at 118 and is connected to the air storage tank 110 by conduit 120, and to the suction control means 92 by conduit 122. The three-way solenoid valve 118 includes a venting port as indicated at 124 to vent the same to atmosphere.

An oil air tank bleeddown valve is indicated at 126 as is connected to the demister 106 by conduit 128, and to the conduit 122 by a conduit 130.

A bleed conduit 132 comprising a restriction as indicated at 133 interposed therein, extends as shown from the oil air tank bleeddown valve 126 into communication with the suction control means 92 at a location in the latter upstream of the closure disc 94, whereby is believed made clear that the said bleed conduit extends into communication with the atmosphere through the air inlet filter means 100.

An air injection conduit 134 extends as shown from the oil air tank bleeddown valve 126 into communication with the suction control means 92 but at a location in the latter downstream of the closure disc 96, whereby is believed made clear that the said air injection conduit extends into communication with the inlet ports of the rotary compressor 90. A check valve 136 is interposed as shown in the air injection line 134 to prevent flow therethrough in the direction of the said bleeddown valve.

A normally open pressure responsive switch is indicated at PS-C and is connected by conduit 138 to the oil air tank 104 so as to be responsive to the pressure in the latter,

The control circuit for the rotary compressor control system of FIG. 3 is depicted in FIG. 4 and may be seen to include normally closed contacts 140 of the pressure switch PS-B, the valve-operating solenoid 142 of the three-way solenoid valve 118, and suitable motor starter interlock means 144, to break current to the solenoid on shutdown to bleed the unit respectively connected as shown in series across the line sources 150 and 152 by leads-146 and 148. Further included-in this control circuit are the normally closed contacts 154 and 156 of suitable, motor overload safety devices, the normally closed contacts 158 of the-temperature responsive switch means 108, the compressor motor starter means 160, and the pole 162 and constant speed contact 164 of a two-position selector switch 166, respectively, all of which are connectable in series across the said line sources by leads 168 and 170, and the switch pole 162, when. the selector switch 166 is in the constant speed position thereof.

The remaining normally closed contacts 172 of the normally closed pressure switch PS-B, and the start-stop contact 174 of the selector switch 166 are connected in series as shown by lead 176, and the normally closed contacts 178 of the normally closed pressure switch PS-C are connected as shown in parallel with normally closed contacts 172 by lead 180. As a result it may be understood that the paralleLconnected contacts 172 and 178 may be connected in series with the motor starter 160 and the respective contacts 158, 156 and 154, respectively, across the line sources 152 and 150 through leads 146, 180, 176, the selector switch pole 162 and lead 170 when the selector switch 166 is in the start-stop position thereof.

The three-way solenoid valve 118 is arranged in the flow diagram of FIG. 3 to connect conduits 120 and 122 when the valve-operating solenoid 142 is deenergized to supply a pressure signal from the air storage tank to the suction control means 92 to close the closure disc 94 and unload the compressor 90. Concomitantly, deenergization of the valve-operating solenoid 142 will result in the said valve connecting conduits and supplying a pressure signal to the oil air tank bleeddown valve 126 to open the latter to connect conduit 128 with each of restricted bleed conduit 132 and air injection conduit 134, it being noted that the conduits 132 and 134 are preferably connected to the same bleeddown valve port to simplify the latter.

Conversely, with the valve-operating solenoid 142 energized, three-way solenoid valve 118 is arranged to vent conduit I22, and accordingly conduit 130, to atmosphere through vent port 124 with the result that the compressor suction control means 92 will reopen to reload the compressor 90, while the bleeddown of the oil air tank 104 through restricted bleed conduit 132 is terminated by the closure of bleeddown valve 126.

OPERATION For representative operation of the rotary compressor control system of FIGS. 3 and 4 as, for example, in the control of a rotary compressor 90 which takes the form of the RS Mono Rotor Air Compressor as mentioned hereinabove, it may be understood that pressure switch PS-B would be set to open the respective normally closed contacts and 172 thereof when the pressure in air storage tank 110 assumed a predetermined maximum in the order, for example, of l15l20 p.s.i., and to reclose the said contacts when the said pressure assumed a predetermined minimum in the same range but somewhat lower than said predetermined maximum. In like manner, pressure switch PS-C would be set to close the normally open contacts 178 thereof when the pressure in the oil air tank exceeded a predetermined'minimum in the order, for example, of 2025 p.s.i., and to reclose the said contacts when the said pressure returned to the said predetermined minumum. In addition, for such use the restriction 133 in bleed conduit 132 would be sized to provide a bleeddown time of approximately 2 to 3 minutes for the bleeddown of the oil air tank from the 115-120 p.s.i. range to the 2025 p.s.i. range.

With the two-position selector switch 166 set in the startstop position thereof, and the rotary compressor 90 operating under loaded conditions, it may be understood that as the pressure within air storage tank 110 assumes the predetermined maximum as discussed above, pressure switch PS-B will function in response thereto to open the normally closed switch contacts 140 and 172, with the effect of the former being to deenergize the valve-operating solenoid 142 of the three-way valve 118 with resultant supply of pressure signals from the air storage tank 110 on conduits 130 and 122 to the oil air tank bleeddown valve 126 and the suction control means 92, respectively. The opening of normally closed contacts 172 will, however, have no immediate effect on compressor operation since the compressor motor starter means will remain energized through closed contacts 178 of PS-B in parallel line 180, whereby the compressor motor will continue to run.

The pressure signal to the suction control means 92 will function to unload the compressor 90 through closure of the closure disc 94, while the pressure signal to bleeddown valve 126 will function to commence the bleeddown of air from the oil air tank through restricted bleed conduit 132 to atmosphere through the suction control means 92 and the air inlet filter means 100, and will function to commence the injection of air form the said oil air tank through injection conduit 134 into the compressor inlet ports downstream of the now closed closure disc 94. As a result of this air injection, it

may be understood that some flow of air will be retained through the compressor 90 despite the fact that the same istive pressure in the oil air tank 1G4 to in turn insure the continuaunce of satisfactory compressor lubrication to significant advantage, and will, in addition, insure the continued effectiveness of the temperature responsive switch means 108 by providing for the continued, albeit markedly reduced, flow of compressed air over the switch temperature sensing means, again to significant advantage.

The bleeddown of the oil air tank 104 to atmosphere through the restricted bleed conduit 132, the suction control means 92, and the air inlet filter means 100, rather than directly to atmosphere, will, or" course, substantially attenuate the bleeddown noise level to significant advantage, while the continued flow of air through the compressor 90 from air injection line 134 also substantially attenuate the change in pitch of the operational noise of the said compressor as the same changes from loaded to unloaded operation.

Unloaded operation of the compressor 90 will continue for the period of time discussed above until the pressure in oil air tank 164 is bled down to the predetermined minimum, also as discussed above, whereupon the ciosed contacts 178 of the pressure responsive switch PS-C will open to deenergize the motor starter 160 and discontinue operation of the compressor 90. Accordingly is believed made clear that the provision of pressure switch PS-C, and the connection of the closed contacts 178 thereof in parallel with normally open contacts 172 of PS-B will positively prevent stopping of the compressor motor until the oil air tank 104 has been bied down to the said predetermined minumum pressure to thus positively prevent the compressor motor from having to restart the compressor 90 against a high-pressure load with resultant possibility of compressor blade damage and high initial torque and electrical power demand as discussed hereinabove. Put another way, it may be understood that since the oil air tank 104 must, of necessity, be bled down before the compressor motor stops, and since there is no way to repressurize the said oil air tank short of compressor motor operation, compressor restarts requiring high initial torque are rendered impossible.

In addition, it believed clear that since the compressor motor is maintained operative by the closed contacts 178 of PS-C, circumstances in the nature of an immediate large scale demand for compressed air from the air storage tank 110, to the extent that the pressure therein frequently and quickly falls below said predetermined minumum, will be ineffective to immediately restart the compressor motor for the simple reason that the same is still running, whereby may be understood that excessive restarting of the latter is substantially inhibited.

Without such immediate, large scale demand for compresmd air, it may be understood that the control system will remain as described until the pressure in the air storage tank 110 falls below said predetermined minimum, at which time the contacts 172 and 140 of PS-B will reclose to respectively reenergize the motor starter means 16-0 to restart the compressor 90, and coneomitantly reenergize the valve-operating solenoid 142 to terminate the supply of pressure signals to the suction control means 92 and the bleeddown valve 126 with the results that the compressor 90 will be reloaded and the bleeddown and injection of air through conduits 132 and 134 terminated.

Operation of the control system of FIGS. 3 and 4 with the selector switch 166 in the constant speed position as may, for example, be required by the fact that excessive restarting of the compressor motor during the course of daily operation might occur despite the provision of the 2 to 2.5 minute time delay by restricted bleed conduit 132, wouid be substantially the same as above with the obvious exception that the system would never be effective to stop the motor of the rotary compressor 90. It is believed equally obvious, however, that the significant advantages enumerated hereinabove in addition to those related to the prevention of excessive compressor motor restarting would continue to be provided by the new and improved control system of the invention.

Referring now to the form of the invention depicted in FIGS. 5, 6 and 7, it may be understood that the same is substantially identical to that depicted in FIGS. 3 and 4 whereby like reference numerals are utilized to identify like system components of the former.

In the system of FIGS. 5, 6 and 7, however, the fixed restriction 133 in bleed line 132 is replaced as indicated by a controlled restriction bleeddown valve 190 which, as illustrated in cross section in FIG. 6, comprises an outer valve body 192 having a stepped port 194 extending therethrough. An inner valve body 196 is slidably disposed as shown in the port 194 and biased toward the inlet end 198 of the latter by a compression spring 200. A restricted valve port 202 is formed to extend as shown through the inner valve body 196.

In operation of the control system of FIGS. 5, 6 and 7, which operation is substantially identical to that of the control system of FIGS. 3 and 4, it may be understood that immediately upon the opening of the oil air tank bleeddown valve 126 to connect conduit 128 to the bleeddown conduit 132, the controlled restriction bleeddown valve 190 will open, as by the slidabie movement of the inner valve body 196 from the position thereof of FIG. 6 to the position thereof of FIG. 7 to enable the substantially rapid passage of air from the oil air tank 104 through both the resultant space 204 between the said outer and inner valve bodies, and the restricted valve port 202 of the latter, respectively.

Once the pressure in the said oil air tank has fallen below a certain levei, in the range for example of 37 to 44 p.s.i. as determined by the force constant of the compression spring 200, the controlled restriction bleeddown valve 190 will return to the position thereof of FIG. 6 whereby the passage of air therethrough can occur only through restricted valve port 202.

By the provision of the controlled restriction bleeddown valve 19 it may be understood that rapid oil air tank bleeddown to a low compressor power consumption level may be achieved, followed by controlled oil air tank bleeddown through restricted valve port 202 to establish the predetermined oil air tank bleeddown time as discussed hereinabove.

In instances wherein the rotary compressor system is marketed without an air storage tank 110, it is believed clear that each of conduits 116 and would be suitably connected in compressor discharge means in the nature of conduit 112 so as to insure that pressure switch PS-B would remain effective to accurately sense compressor discharge pressure, while conduit 120 would remain efiective to supply the requisite pressure signals for application through the three-way solenoid valve 118 as described.

While there have been shown and described preferred embodiments of the invention, it will be understood that the invention may be embodied otherwise than as herein specifically illustrated or described, and that in the illustrated embodi ments certain changes in the details of construction and in the form and arrangement of the parts may be made without departing from the underlying ideal and principals of this invention within the scope of the appended claims.

What I claim is:

1. In a compressor control system for use with a motor driven compressor including compressor suction control means which are operable to load and unload said compressor, oil air tank means connected to the compressor discharge, air storage tank means connected to the discharge of said oil air tank means, and control means operatively associated with said air storage tank means and said compressor motor, and operable to respectively operate said suction control means to unload said compressor, and to start and stop operation of said compressor motor, in response to the pressure said air storage tank means; the improvements comprising, bleeddown means operatively associated with said oil air tank means and operable in response to compressor-unioading operation of said control means to bleeddown said oil air tank means at a predetermined rate, and means operatively associated with said oil air tank means and said compressor motor, respectively, and responsive to the pressure in the former to prevent stopping of said compressor motor by said control means until the pressure in said oil air tank means has been bled down to a predetermined level, whereby immediate restarting of said compressor against a high high-pressure in said oil air tank is prevented.

2. In a compressor control system as in claim I; said improvements further comprising, air injection means operatively associated with said oil air tank means and operable in response to compressor-unloading operation of said control means to inject air from said oil air tank means into the suction of said compressor during unloaded operation thereof to maintain a flow of air therethrough to prevent bleeddown of said oil air tank to atmospheric pressure to insure adequate compressor lubrication.

3. In a compressor control system as in claim I wherein said bleeddown means comprise a restricted conduit in fluid flow communication with said oil air tank means.

4. In a compressor control system as in claim 2 wherein said bleeddown means comprise a restricted conduit in fluid flow communication with said oil air tank means.

5. In a compressor control system as in claim 1 wherein said bleeddown means are effective to bleeddown said oil air tank through said compressor suction control means tosubstantially attenuate the noise attendant oil air tank bleeddown.

6. In a compressor control system as in claim 2 wherein said bleeddown means are effective to bleeddown said oil air tank through said compressor suction control means to substantially attenuate the noise attendant oil air tank bleeddown.

7. In a compressor control system as in claim 6 wherein said bleeddown means comprise a restricted conduit in fluid flow communication with said oil air tank means.

8. In a compressor control system as in claim 1 wherein, said bleeddown means comprise variable rate bleeddown means which are operable to bleeddown said oil air tank at varying rates in accordance with the pressure in the latter.

9. In a compressor control system as in claim 2 wherein, said bleeddown means comprise variable rate bleeddown means which are operable to bleeddown said oil air tank at varying rates in accordance with the pressure in the latter.

10. In a compressor control system as in claim 5 wherein, said bleeddown means comprise variable rate bleeddown means which are operable to bleeddown said oil air tank at varying rates in accordance with the pressure in the latter.

I]. In a compressor control system as in claim 6 wherein, said bleeddown means comprise variable rate bleeddown means which are operable to bleeddown said oil air tank at varying rates in accordance with the pressure in the latter.

12. In a compressor control system as in claim 8 wherein, said variable rate bleeddown means comprise a controlled restriction bleeddown valve in the fluid flow communication with said oil air tank means, said valve including an outer valve body and an inner valve body having first and second relative positions, said valve being operable to bleeddown said oil air tank at a different rate when said valve bodies are in said first relative positions than when the same are in said second relative positions.

13. In a compressor control system as in claim 10 wherein, said variable rate bleeddown means comprise a controlled restriction bleeddown valve in the fluid flow communication with said oil air tank means, said valve including an outer valve body and an inner valve body having first and second relative positions, said valve being operable to bleeddown said oil air tank at a different rate when said valve bodies are in said first relative positions than when the same are in said second relative positions.

14. In a compressor control system as in claim 1 wherein, said control means comprise first pressure switch means having normally closed contacts and being responsive to the pressure in said air storage tank to open said contacts only when said pressure assumes a predetermined level, said means operatively associated with said oil air tank means comprise second pressure switch means having normally closed contacts and being operable to open the same only when the pressure in said oil air tank means assumes a predetermined level, series connected energization circuit means for said compressor motor, and means connecting said first and second pressure switch means contacts in parallel in said series connected energization circuit means whereby, energization of said compressor motor will be continued albeit the opening of said first pressure switch means contacts until the opening of said second pressure switch means contacts.

15. In a compressor control system as in claim 2 wherein, said control means comprise first pressure switch means having normally closed contacts and being responsive to the pressure in said air storage tank to open said contacts only when said pressure assumes a predetermined level, said means operatively associated with said oil air tank means comprise second pressure switch means having normally closed contacts and being operable to open the same only when the pressure in said oil air tank means assumes a predetermined level, series connected energization circuit means for said compressor motor, and means connecting said first and second pressure switch means contacts in parallel in said series connected energization circuit means whereby, energization of said com- 7 said control means comprise first pressure switch means having normally closed contacts and being responsive to the pressure in said air storage tank to open said contacts only when said pressure assumes a predetermined level, said means operatively associated with said oil air tank means comprise second pressure switch means having normally closed contacts and being operable to open the same only when the pressure in said oil air tank means assumes a predetermined level, series connected energization circuit means for said compressor motor, and means connecting said first and second pressure switch means contacts in parallel in said series connected energization circuit means whereby, energization of said compressor motor will be continued albeit the opening of said first pressure switch means contacts until the opening of said second pressure switch means contacts.

17. In a compressor control system as in claim 8 wherein, said control means comprise first pressure switch means having normally closed contacts and being responsive to the pressure in said air storage tank to open said contacts only when said pressure assumes a predetermined level, said means operatively associated with said oil air tank means comprise second pressure switch means having normally closed contacts and being operable to open the same only when the pressure in said oil air tank means assumes a predetermined level, series connected energization circuit means for said compressor motor, and means connecting said first and second pressure switch means contacts in parallel in said series connected energization circuit means whereby, energization of said compressor motor will be continued albeit the opening of said first pressure switch means contacts until the opening of said second pressure switch means contacts.

18. In a compressor control system for use with a motor driven compressor including compressor inlet suction control means which are operable to load and unload said compressor, oil air tank means connected to the compressor discharge, air storage tank means connected to the discharge of said oil air tank means, and control means operatively associated with said air storage tank means and said compressor motor, and operable to respectively operate said suction control means to unload said compressor, and to start and stop operation of said compressor motor, in response to the pressure in said air storage tank means; the improvements comprising, air injection means operatively associated with said oil air tank means and operable in response to compressor unloading operation of said control means to inject air from said oil air tank means into the inlet of said compressor downstream of the suction control means during initial unloaded operation thereof to prevent sudden changes of operational load on the compressor.

19. In a compressor control system as in claim 18; said improvements further comprising, bleeddown means operatively associated with said oil air tank means and operable in response to compressor-unloading operation of said control means to bleeddown said oil air tank means at a predetermined rate.

20. In a compressor control system as in claim 19 wherein; said bleeddown means are effective to bleeddown said oil air tank through said compressor suction control means to substantially attenuate the noise attendant oil air tank bleeddown.

21. A compressor assembly comprising:

a compressor having an inlet and an outlet;

a motor operatively associated with said compressor to drive said compressor;

conduit means connected to said outlet of said compressor to carry the discharge of said compressor;

means to unload said compressor by throttling the inlet thereof, operatively associated with the inlet of said compressor;

control means operatively associated with said compressor discharge conduit means and said motor to actuate said compressor unloading means and to start and stop said motor in response to the pressure in said compressor discharge conduit means;

bleeddown means operatively communicated with said compressor discharge conduit means and the compressor inlet and actuated by said compressor unloading means to inject a portion of the compressor discharge into the inlet and through the compressor while bleeding down said compressor discharge conduit means at a predetermined rate;

said control means including means to continue operation of said motor until the pressure in said compressor discharge conduit means has been bled down below a predetermined value, so that immediate restarting of said compressor against a high-pressure load in said compressor discharge conduit means is prevented.

22. A compressor assembly comprising:

a compressor having an inlet and an outlet;

a motor operatively associated with said compressor to drive said compressor;

receiving means connected to said outlet of said compressor to receive the discharge of said compressor;

means operatively associated with the inlet of said compressor to unload said compressor by throttling the inlet thereof;

control means operatively associated with said compressor discharge receiving means and said motor to actuate said compressor unloading means and to start and stop said motor in response to the pressure in said compressor discharge receiving means;

bleeddown means communicating with said compressor discharge receiving means and actuated by said compressor unloading means to bleeddown said compressor discharge receiving means at a predetermined rate; and

injecting means connected with the compressor discharge receiving means and the compressor inlet for injecting a limited portion of the compressor discharge into the compressor during bleeddown;

said control means including means to delay stopping of the compressor motor after unloading of the compressor to prevent immediate restarting of the motor against high pressure in the compressor discharge receiving means. 

1. In a compressor control system for use with a motor driven compressor including compressor suction control means which are operable to load and unload said compressor, oil air tank means connected to the compressor discharge, air storage tank means connected to the discharge of said oil air tank means, and control means operatively associated with said air storage tank means and said compressor motor, and operable to respectively operate said suction control means to unload said compressor, and to start and stop operation of said compressor motor, in response to the pressure in said air storage tank means; the improvements comprising, bleeddown means operatively associated with said oil air tank means and operable in response to compressor-unloading operation of said control means to bleeddown said oil air tank means at a predetermined rate, and means operatively associated with said oil air tank means and said compressor motor, respectively, and responsive to the pressure in the former to prevent stopping of said compressor motor by said control means until the pressure in said oil air tank means has been bled down to a predetermined level, whereby immediate restarting of said compressor against a high high-pressure in said oil air tank is prevented.
 2. In a compressor control system as in claim 1; said improvements further comprising, air injection means operatively associated with said oil air tank means and operable in response to compressor-unloading operation of said control means to inject air from said oil air tank means into the suction of said compressor during unloaded operation thereof to maintain a flow of air therethrough to prevent bleeddown of said oil air tank to atmospheric pressure to insure adequate compressor lubrication.
 3. In a compressor control system as in claim 1 wherein said bleeddown means comprise a restricted conduit in fluid flow communication with said oil air tank means.
 4. In a compressor control system as in claim 2 wherein said bleeddown means comprise a restricted conduit in fluid flow communication with said oil air tank means.
 5. In a compressor control system as in claim 1 wherein said bleeddown means are effective to bleeddown said oil air tank through said compressor suction control means to substantially attenuate the noise attendant oil air tank bleeddown.
 6. In a compressor control system as in claim 2 wherein said bleeddown means are effective to bleeddown said oil air tank through said compressor suction control means to substantially attenuate the noise attendant oil air tank bleeddown.
 7. In a compressor control system as in claim 6 wherein said bleeddown means comprise a restricted conduit in fluid flow communication with said oil air tank means.
 8. In a compressor control system as in claim 1 wherein, said bleeddown means comprise variable rate bleeddown means which are operable to bleeddown said oil air tank at varying rates in accordance with the pressure in the latter.
 9. In a compRessor control system as in claim 2 wherein, said bleeddown means comprise variable rate bleeddown means which are operable to bleeddown said oil air tank at varying rates in accordance with the pressure in the latter.
 10. In a compressor control system as in claim 5 wherein, said bleeddown means comprise variable rate bleeddown means which are operable to bleeddown said oil air tank at varying rates in accordance with the pressure in the latter.
 11. In a compressor control system as in claim 6 wherein, said bleeddown means comprise variable rate bleeddown means which are operable to bleeddown said oil air tank at varying rates in accordance with the pressure in the latter.
 12. In a compressor control system as in claim 8 wherein, said variable rate bleeddown means comprise a controlled restriction bleeddown valve in the fluid flow communication with said oil air tank means, said valve including an outer valve body and an inner valve body having first and second relative positions, said valve being operable to bleeddown said oil air tank at a different rate when said valve bodies are in said first relative positions than when the same are in said second relative positions.
 13. In a compressor control system as in claim 10 wherein, said variable rate bleeddown means comprise a controlled restriction bleeddown valve in the fluid flow communication with said oil air tank means, said valve including an outer valve body and an inner valve body having first and second relative positions, said valve being operable to bleeddown said oil air tank at a different rate when said valve bodies are in said first relative positions than when the same are in said second relative positions.
 14. In a compressor control system as in claim 1 wherein, said control means comprise first pressure switch means having normally closed contacts and being responsive to the pressure in said air storage tank to open said contacts only when said pressure assumes a predetermined level, said means operatively associated with said oil air tank means comprise second pressure switch means having normally closed contacts and being operable to open the same only when the pressure in said oil air tank means assumes a predetermined level, series connected energization circuit means for said compressor motor, and means connecting said first and second pressure switch means contacts in parallel in said series connected energization circuit means whereby, energization of said compressor motor will be continued albeit the opening of said first pressure switch means contacts until the opening of said second pressure switch means contacts.
 15. In a compressor control system as in claim 2 wherein, said control means comprise first pressure switch means having normally closed contacts and being responsive to the pressure in said air storage tank to open said contacts only when said pressure assumes a predetermined level, said means operatively associated with said oil air tank means comprise second pressure switch means having normally closed contacts and being operable to open the same only when the pressure in said oil air tank means assumes a predetermined level, series connected energization circuit means for said compressor motor, and means connecting said first and second pressure switch means contacts in parallel in said series connected energization circuit means whereby, energization of said compressor motor will be continued albeit the opening of said first pressure switch means contacts until the opening of said second pressure switch means contacts.
 16. In a compressor control system as in claim 5 wherein, said control means comprise first pressure switch means having normally closed contacts and being responsive to the pressure in said air storage tank to open said contacts only when said pressure assumes a predetermined level, said means operatively associated with said oil air tank means comprise second pressure switch means having normally closed contacts and being operable to open the sAme only when the pressure in said oil air tank means assumes a predetermined level, series connected energization circuit means for said compressor motor, and means connecting said first and second pressure switch means contacts in parallel in said series connected energization circuit means whereby, energization of said compressor motor will be continued albeit the opening of said first pressure switch means contacts until the opening of said second pressure switch means contacts.
 17. In a compressor control system as in claim 8 wherein, said control means comprise first pressure switch means having normally closed contacts and being responsive to the pressure in said air storage tank to open said contacts only when said pressure assumes a predetermined level, said means operatively associated with said oil air tank means comprise second pressure switch means having normally closed contacts and being operable to open the same only when the pressure in said oil air tank means assumes a predetermined level, series connected energization circuit means for said compressor motor, and means connecting said first and second pressure switch means contacts in parallel in said series connected energization circuit means whereby, energization of said compressor motor will be continued albeit the opening of said first pressure switch means contacts until the opening of said second pressure switch means contacts.
 18. In a compressor control system for use with a motor driven compressor including compressor inlet suction control means which are operable to load and unload said compressor, oil air tank means connected to the compressor discharge, air storage tank means connected to the discharge of said oil air tank means, and control means operatively associated with said air storage tank means and said compressor motor, and operable to respectively operate said suction control means to unload said compressor, and to start and stop operation of said compressor motor, in response to the pressure in said air storage tank means; the improvements comprising, air injection means operatively associated with said oil air tank means and operable in response to compressor unloading operation of said control means to inject air from said oil air tank means into the inlet of said compressor downstream of the suction control means during initial unloaded operation thereof to prevent sudden changes of operational load on the compressor.
 19. In a compressor control system as in claim 18; said improvements further comprising, bleeddown means operatively associated with said oil air tank means and operable in response to compressor-unloading operation of said control means to bleeddown said oil air tank means at a predetermined rate.
 20. In a compressor control system as in claim 19 wherein; said bleeddown means are effective to bleeddown said oil air tank through said compressor suction control means to substantially attenuate the noise attendant oil air tank bleeddown.
 21. A compressor assembly comprising: a compressor having an inlet and an outlet; a motor operatively associated with said compressor to drive said compressor; conduit means connected to said outlet of said compressor to carry the discharge of said compressor; means to unload said compressor by throttling the inlet thereof, operatively associated with the inlet of said compressor; control means operatively associated with said compressor discharge conduit means and said motor to actuate said compressor unloading means and to start and stop said motor in response to the pressure in said compressor discharge conduit means; bleeddown means operatively communicated with said compressor discharge conduit means and the compressor inlet and actuated by said compressor unloading means to inject a portion of the compressor discharge into the inlet and through the compressor while bleeding down said compressor discharge conduit means at a predetermined rate; said control means including means to Continue operation of said motor until the pressure in said compressor discharge conduit means has been bled down below a predetermined value, so that immediate restarting of said compressor against a high-pressure load in said compressor discharge conduit means is prevented.
 22. A compressor assembly comprising: a compressor having an inlet and an outlet; a motor operatively associated with said compressor to drive said compressor; receiving means connected to said outlet of said compressor to receive the discharge of said compressor; means operatively associated with the inlet of said compressor to unload said compressor by throttling the inlet thereof; control means operatively associated with said compressor discharge receiving means and said motor to actuate said compressor unloading means and to start and stop said motor in response to the pressure in said compressor discharge receiving means; bleeddown means communicating with said compressor discharge receiving means and actuated by said compressor unloading means to bleeddown said compressor discharge receiving means at a predetermined rate; and injecting means connected with the compressor discharge receiving means and the compressor inlet for injecting a limited portion of the compressor discharge into the compressor during bleeddown; said control means including means to delay stopping of the compressor motor after unloading of the compressor to prevent immediate restarting of the motor against high pressure in the compressor discharge receiving means. 